System and head for continuously manufacturing composite structure

ABSTRACT

A print head is disclosed for use with an additive manufacturing system. The head may have a matrix reservoir, and a nozzle base disposed downstream of the matrix reservoir. The nozzle base may include an opening configured to receive a plurality of continuous reinforcements coated in a liquid matrix. The print head may also have a cover configured to engage the nozzle base and close off a side of the opening, and a guide removably receivable within at least one of the nozzle base and the cover. The guide may include at least one divider configured to axially divide the opening into a plurality of adjacent channels that each receive at least one of the plurality of continuous reinforcements. The print head may further have a cure enhancer mounted at a trailing side of the nozzle base opposite the cover and configured to expose the matrix coating on the plurality of continuous reinforcements to a cure energy.

RELATED APPLICATIONS

This application is based on and claims the benefit of priority from U.S. Provisional Application No. 62/730,541 that was filed on Sep. 13, 2018, the contents of which are expressly incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to a manufacturing system and, more particularly, to a system and head for continuously manufacturing composite structures.

BACKGROUND

Continuous fiber 3D printing (a.k.a., CF3D™) involves the use of continuous fibers embedded within a matrix discharging from a moveable print head. The matrix can be a traditional thermoplastic, a powdered metal, a liquid resin (e.g., a UV curable and/or two-part resin), or a combination of any of these and other known matrixes. Upon exiting the print head, a head-mounted cure enhancer (e.g., a UV light, an ultrasonic emitter, a heat source, a catalyst supply, etc.) is activated to initiate and/or complete curing of the matrix. This curing occurs almost immediately, allowing for unsupported structures to be fabricated in free space. When fibers, particularly continuous fibers, are embedded within the structure, a strength of the structure may be multiplied beyond the matrix-dependent strength. An example of this technology is disclosed in U.S. Pat. No. 9,511,543 that issued to Tyler on Dec. 6, 2016 (“the '543 patent”).

Although CF3D™ provides for increased strength, compared to manufacturing processes that do not utilize continuous fiber reinforcement, improvements can be made to the structure and/or operation of existing systems. The disclosed additive manufacturing system is uniquely configured to provide these improvements and/or to address other issues of the prior art.

SUMMARY

In one aspect, the present disclosure is directed to a nozzle assembly for a print head of an additive manufacturing system. The nozzle assembly may include a nozzle base having an opening configured to receive a plurality of continuous reinforcements, and a cover configured to engage the nozzle base and close off a side of the opening. The nozzle assembly may also include a guide removably receivable within at least one of the nozzle base and the cover. The guide may have at least one divider configured to axially divide the opening into a plurality of adjacent channels that each receive at least one of the plurality of continuous reinforcements.

In another aspect, the present disclosure is directed to a print head for an additive manufacturing system. The print head may include matrix reservoir, and a nozzle base disposed downstream of the matrix reservoir. The nozzle base may include an opening configured to receive a plurality of continuous reinforcements coated in a liquid matrix. The print head may also have a cover configured to engage the nozzle base and close off a side of the opening, and a guide removably receivable within at least one of the nozzle base and the cover. The guide may include at least one divider configured to axially divide the opening into a plurality of adjacent channels that each receive at least one of the plurality of continuous reinforcements. The print head may further have a cure enhancer mounted at a trailing side of the nozzle base opposite the cover and configured to expose the matrix coating on the plurality of continuous reinforcements to a cure energy

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of and exemplary disclosed additive manufacturing system;

FIG. 2 is a cross-sectional illustration of an exemplary disclosed nozzle assembly that may be utilized with the system of FIG. 1;

FIG. 3 is an exploded view illustration of the nozzle assembly of FIG. 2; and

FIGS. 4-7 are diagrammatic illustrations of exemplary guide inserts that may be utilized with the nozzle assembly of FIG. 2.

DETAILED DESCRIPTION

FIG. 1 illustrates an exemplary system 10, which may be used to continuously manufacture a composite structure 12 having any desired cross-sectional shape (e.g., ellipsoidal, polygonal, etc.). System 10 may include at least a moveable support 14 and a print head (“head”) 16. Head 16 may be coupled to and moved by support 14. In the disclosed embodiment of FIG. 1, support 14 is a robotic arm capable of moving head 16 in multiple directions during fabrication of structure 12, such that a resulting longitudinal axis of structure 12 is three-dimensional. It is contemplated, however, that support 14 could alternatively be an overhead gantry or a hybrid gantry/arm also capable of moving head 16 in multiple directions during fabrication of structure 12. Although support 14 is shown as being capable of multi-axis (e.g., six or more axes) movement, it is contemplated that any other type of support 14 capable of moving head 16 in the same or in a different manner could also be utilized, if desired. In some embodiments, a drive may mechanically couple head 16 to support 14 and may include components that cooperate to move and/or supply power or materials to head 16.

Head 16 may be configured to receive or otherwise contain a matrix. The matrix may include any type of material (e.g., a liquid resin, such as a zero-volatile organic compound resin; a powdered metal; etc.) that is curable. Exemplary matrixes include thermosets, single- or multi-part epoxy resins, polyester resins, cationic epoxies, acrylated epoxies, urethanes, esters, thermoplastics, photopolymers, polyepoxides, thiols, alkenes, thiol-enes, reversible resins (e.g., Triazolinedione, a covalent-adaptable network, a spatioselective reversible resin, etc.) and more. In one embodiment, the matrix inside head 16 may be pressurized, for example by an external device (e.g., an extruder or another type of pump—not shown) that is fluidly connected to head 16 via a corresponding conduit (not shown). In another embodiment, however, the matrix pressure may be generated completely inside of head 16 by a similar type of device. In yet other embodiments, the matrix may be gravity-fed through and/or mixed within head 16. In some instances, the matrix inside head 16 may need to be kept cool and/or dark to inhibit premature curing; while in other instances, the matrix may need to be kept warm for similar reasons. In either situation, head 16 may be specially configured (e.g., insulated, chilled, and/or warmed) to provide for these needs.

The matrix may be used to coat, encase, or otherwise at least partially surround (e.g., wet) any number of continuous reinforcements (e.g., separate fibers, tows, rovings, ribbons, and/or sheets of material) and, together with the reinforcements, make up at least a portion (e.g., a wall) of composite structure 12. The reinforcements may be stored within (e.g., on separate internal spools—not shown) or otherwise passed through head 16 (e.g., fed from one or more external spools—not shown). When multiple reinforcements are simultaneously used, the reinforcements may be of the same type and have the same diameter and cross-sectional shape (e.g., circular, square, flat, hollow, solid, etc.), or of a different type with different diameters and/or cross-sectional shapes. The reinforcements may include, for example, carbon fibers, vegetable fibers, wood fibers, mineral fibers, glass fibers, metallic wires, optical tubes, etc. It should be noted that the term “reinforcement” is meant to encompass both structural and non-structural types of continuous materials that can be at least partially encased in the matrix discharging from head 16.

The reinforcements may be exposed to (e.g., coated with) the matrix while the reinforcements are inside head 16, while the reinforcements are being passed to head 16 (e.g., as a prepreg material), and/or while the reinforcements are discharging from head 16, as desired. The matrix, dry reinforcements, and/or reinforcements that are already exposed to the matrix (e.g., wetted reinforcements) may be transported into head 16 in any manner apparent to one skilled in the art.

The matrix and reinforcement may be discharged from a nozzle assembly 18 of head 16 via at least two different modes of operation. In a first mode of operation, the matrix and reinforcement are extruded (e.g., pushed under pressure and/or mechanical force) from nozzle assembly 18, as head 16 is moved by support 14 to create the 3-dimensional shape of structure 12. In a second mode of operation, at least the reinforcement is pulled from nozzle assembly 18, such that a tensile stress is created in the reinforcement during discharge. In this mode of operation, the matrix may cling to the reinforcement and thereby also be pulled from nozzle assembly 18 along with the reinforcement, and/or the matrix may be discharged from nozzle assembly 18 under pressure along with the pulled reinforcement. In the second mode of operation, where the matrix material is being pulled from head 16 with the reinforcement, the resulting tension in the reinforcement may increase a strength of structure 12 (e.g., by aligning the reinforcements, inhibiting buckling, equally distributing loads, etc.), while also allowing for a greater length of unsupported structure 12 to have a straighter trajectory (e.g., by creating moments that oppose gravity).

The reinforcement may be pulled from nozzle assembly 18 as a result of head 16 moving away from an anchor point 20. In particular, at the start of structure-formation, a length of matrix-impregnated reinforcement may be pulled and/or pushed from nozzle assembly 18, deposited onto a stationary anchor point 20, and cured, such that the discharged material adheres to anchor point 20. Thereafter, head 16 may be moved away from anchor point 20, and the relative movement may cause additional reinforcement to be pulled from nozzle assembly 18. It should be noted that the movement of the reinforcement through head 16 could be assisted (e.g., via internal feed mechanisms), if desired. However, the discharge rate of the reinforcement from nozzle assembly 18 may primarily be the result of relative movement between head 16 and anchor point 20, such that tension is created within the reinforcement.

Nozzle assembly 18 may be fluidly connected to a matrix reservoir 22. Although matrix reservoir 22 is shown as being at least partially inside of head 16, it should be noted that matrix reservoir 22 and/or another wetting mechanism could alternatively be located separately from (e.g., upstream of) head 16. Nozzle assembly 18 may be a generally cylindrical component having an upstream or base end in communication with matrix reservoir 22, a downstream or discharge tip, and one or more passages that extend from the base end to the tip end.

Any number of reinforcements (represented as “R” in FIG. 2) may be passed axially through reservoir 22 (or another wetting mechanism—not shown), where at least some matrix-wetting occurs (matrix represented as “M” in FIG. 2), and discharged from head 16 via nozzle assembly 18. One or more orifices may be located at the tip end of nozzle assembly 18 to accommodate passage of the matrix-wetted reinforcements. In some embodiments, a single generally circular orifice is utilized. In other embodiments, however, multiple circular orifices may be used to simultaneously discharge multiple separate tows of reinforcement. In addition, orifices of another shape (e.g., a rectangular shape) may allow for printing of ribbons and/or sheets that do not have a circular shape.

One or more cure enhancers (e.g., one or more light sources, ultrasonic emitters, lasers, heaters, catalyst dispensers, microwave generators, etc.) 26 may be mounted proximate head 16 (e.g., around nozzle assembly 18 or only at a trailing side of nozzle assembly 18) and configured to enhance a cure rate and/or quality of the matrix as it is discharged from nozzle assembly 18. Cure enhancer 26 may be controlled to selectively expose internal and/or external surfaces of structure 12 to cure energy (e.g., light energy, electromagnetic radiation, vibrations, heat, a chemical catalyst or hardener, etc.) during the formation of structure 12. The cure energy may increase a rate of chemical reaction occurring within the matrix, sinter the material, harden the material, or otherwise cause the material to cure as it discharges from nozzle assembly 18.

A controller 28 may be provided and communicatively coupled with support 14, head 16, and any number and type of cure enhancers 26. Controller 28 may embody a single processor or multiple processors that include a means for controlling an operation of system 10. Controller 28 may include one or more general- or special-purpose processors or microprocessors. Controller 28 may further include or be associated with a memory for storing data such as, for example, design limits, performance characteristics, operational instructions, matrix characteristics, reinforcement characteristics, characteristics of structure 12, and corresponding parameters of each component of system 10. Various other known circuits may be associated with controller 28, including power supply circuitry, signal-conditioning circuitry, solenoid/motor driver circuitry, communication circuitry, and other appropriate circuitry. Moreover, controller 28 may be capable of communicating with other components of system 10 via wired and/or wireless transmission.

One or more maps may be stored in the memory of controller 28 and used during fabrication of structure 12. Each of these maps may include a collection of data in the form of models, lookup tables, graphs, and/or equations. In the disclosed embodiment, the maps are used by controller 28 to determine desired characteristics of cure enhancers 26, the associated matrix, and/or the associated reinforcements at different locations within structure 12. The characteristics may include, among others, a type, quantity, and/or configuration of reinforcement and/or matrix to be discharged at a particular location within structure 12, and/or an amount, intensity, shape, and/or location of desired curing. Controller 28 may then correlate operation of support 14 (e.g., the location and/or orientation of head 16) and/or the discharge of material from head 16 (a type of material, desired performance of the material, cross-linking requirements of the material, a discharge rate, etc.) with the operation of cure enhancers 26, such that structure 12 is produced in a desired manner.

A cross-section of an exemplary nozzle assembly 18 is disclosed in detail in FIG. 2. As shown in this figure, nozzle assembly 18 may be removably connected to head 16 at a location downstream of matrix reservoir 22. In this example, nozzle assembly 18 is a multi-channel nozzle configured to discharge composite material having a generally rectangular, flat, or ribbon-like cross-section. The configuration of head 16, however, may allow nozzle assembly 18 to be swapped out for another assembly (not shown) that discharges composite material having a different shape (e.g., a circular cross-section, a tubular cross-section, etc.). Fibers, tubes, and/or other reinforcements R may pass through matrix reservoir 22 and be wetted (e.g., at least partially coated and/or fully saturated) with matrix material M prior to discharge.

In the disclosed embodiment, nozzle assembly 18 includes multiple parts arranged in such way that allows access to the reinforcements passing therethrough. This access may be helpful during startup (e.g., for threading of the different reinforcements through nozzle assembly 18), after fabrication completion (e.g., for cleaning purposes), and/or during fabrication (e.g., to clear blockages). As shown in FIGS. 2 and 3, nozzle assembly 18 may include, among other things, a base component (“base”) 29, a removeable cover 30, and a replaceable fiber guide (“guide”) 32. It is contemplated that, in some embodiments, cover 30 and fiber guide 32 could be integrated, if desired.

Base 29 may be generally hollow, having a central opening 34 that fluidly communicates with matrix reservoir 22. Central opening 34 may extend from matrix reservoir to a tip 36 end of nozzle assembly 18 and have any desired shape. Base 29 may be cutaway (e.g., along a plane passing through an axis of base 29 in the axial direction) at a lower side to expose a portion of central opening 34 to the environment.

Cover 30 may removably engage base 29 at the exposed side of central opening 34 to close off the exposed side. In one embodiment, cover 30 is generally L-shaped, such that central opening 34 steps down to a smaller cross-sectional (e.g., half-circle) area when engaged by cover 30. It should be noted, however, that cover 30 could have another shape and/or that central opening 34 could retain a substantially constant, decreasing, or increasing cross-sectional area of any desired shape. For example, a depth of central opening 34, between cover 30 and base 29 may be greater at an end adjacent matrix reservoir 22 and less at tip 36. Likewise, a width of central opening 34 (e.g., a dimension generally orthogonal to the depth) may be substantially constant, decrease, or increase. One or more fasteners, clasps, magnets, or other mechanisms 40 (shown only in FIG. 2, for clarity) may be used to removably connect cover 30 to base 29. It is contemplated that a sacrificial and/or friction-reducing surface (e.g., a PTFE, PEEK, PPS, Nylon, Acetal, and/or Polyester layer) 42 may be applied to an inner area of cover 30 (e.g., between cover 30 and base 29), in some embodiments. In some embodiments, instead of surface 42 being applied to cover 30, a separate stand-alone component of the same or similar material may be utilized.

Guide 32 may include any number of dividers 44 that are intended to separate one or more reinforcements from adjacent reinforcements passing through nozzle assembly 18. Dividers 44 may extend radially a distance into central opening 34 (e.g., mostly or completely through central opening 34) to create adjacent fiber channels 46, and have any desired length (e.g., a length about equal to or less than a length of the longer leg of L-shaped cover 30). Dividers 44 may be oriented generally parallel with an axis of nozzle assembly 18 and have a depth that is generally orthogonal to the primary surface of cover 30. In some embodiments, dividers 44 taper transversely inward toward the axis of base 29 to facilitate convergence of adjacent reinforcements prior to discharge from tip 36. Dividers 44 may be independent components that are separately assembled into a recess 47 of base 29, or only protrusions that extend from a common back plate 48. In the latter embodiment, dividers 44 and guide 32 may be assembled as a single unit into recess 47. An internal edge 38 of backplate 48 (e.g., at tip 36) may be radiused (see FIG. 3) to reduce breakage of reinforcements passing through nozzle assembly 18. It is also contemplated that dividers 44 could be integral with surface 42, in some embodiments. Guide 32 may be fabricated from a material similar to surface 42, if desired.

Each fiber channel 46 may have a cross-sectional area larger than a cross-sectional area of the reinforcement(s) passing therethrough. For example, each fiber channel 46 may be up to several hundred times larger. In some embodiments, the cross-sectional area may remain substantially constant along the length of channel 46, while in other embodiments the cross-sectional area may increase or decrease. A width and/or a depth of each channel 46 may range from about 0.01 in. to about (e.g., within engineering tolerances) 0.10 in. In one example, the cross-sectional area at an outlet end of each fiber channel 46 may be the smallest portion of channel 46 and sized to provide a desired fiber-to-resin ratio at discharge from nozzle assembly 18. In this example, the outlet functions as a restricted orifice, through which the reinforcement(s), coated with no more than a desired amount of resin, may pass. Any excess resin may be inhibited from passing through the outlet of channel 46 and build up within a remaining upstream volume of channel 46. In this way, channel 46 may function as a mini-reservoir for only the reinforcement(s) passing therethrough.

In some applications, multiple different guides 32 may be swappable within the same nozzle assembly 18. For example, FIG. 4 illustrates guides 32A-32D, each having a different configuration that may provide benefits in different scenarios. For example, guide 32A may have multiple dividers (e.g., three) 44 that divide central opening 34 into at least four adjacent channels 46 lying within a common plane. In this example, dividers 44 and channels 46 are tapered inward (e.g., in a width direction, relative to an axis of base 29) and toward the downstream outlet, causing the associated reinforcements passing therethrough to converge transversely at an outlet of nozzle assembly 18 and create a ribbon of material having a generally rectangular cross-section. A depth of channels 46 may substantially constant in this example, while the width decreases toward the outlet. Both the depth and width may be about equal at the outlet, forming a generally square cross-section.

In another example, guide 32B may also have multiple dividers 44 that divide central opening 34 into multiple adjacent channels 46 lying within a common plane. This example may be similar to the previously discussed example, but with a taper in only the depth direction. The width dimension of guide 32B at the outlet may be larger than the depth dimension at the outlet, thereby forming a generally rectangular cross-section. It is contemplated that the depth dimension may be larger than the width dimension, if desired. It should be noted that, by having one dimension larger than the other, a greater amount of resin may be forced to opposing sides in the larger dimension direction.

In another example, guide 32C may also have multiple dividers 44 that divide central opening 34 into multiple adjacent channels 46 lying within a common plane. However, in this example, the width and depth of channels 46 both taper toward the outlet.

In a final example, guide 32D (also shown in FIG. 3) may also have multiple (e.g., two) dividers 44 that divide central opening 34 into multiple adjacent channels 46 lying within a common plane. However, in this example, channels 46 do not taper in any direction.

It should be noted that guides 32 may have any number of dividers 44 an channels formed therein. In addition, within a single guide 32, each channel 46 could have a different configuration, if desired. For example, independent channels 46 could taper differently, have different cross-sectional areas, and/or different cross-sectional shapes (e.g., circular, square, and/or rectangular). Finally, while all of channels 46 have been described as generally lying within the same plane, it is contemplated that channels 46 could alternatively or additionally be organized into overlapping (aligned, misaligned, and/or random) rows.

INDUSTRIAL APPLICABILITY

The disclosed systems may be used to continuously manufacture composite structures having any desired cross-sectional shape and length. The composite structures may include any number of different fibers of the same or different types and of the same or different diameters, and any number of different matrixes of the same or different makeup. Operation of system 10 will now be described in detail.

At a start of a manufacturing event, information regarding a desired structure 12 may be loaded into system 10 (e.g., into controller 28 that is responsible for regulating operations of support 14 and/or head 16). This information may include, among other things, a size (e.g., diameter, wall thickness, length, etc.), a contour (e.g., a trajectory), surface features (e.g., ridge size, location, thickness, length; flange size, location, thickness, length; etc.), connection geometry (e.g., locations and sizes of couplings, tees, splices, etc.), desired weave patterns, weave transition locations, etc. It should be noted that this information may alternatively or additionally be loaded into system 10 at different times and/or continuously during the manufacturing event, if desired. Based on the component information, one or more different reinforcements and/or matrix materials may be selectively installed and/or continuously supplied into system 10.

To install the reinforcements, cover 30 may need to be removed from base 29 (e.g., by removal of fasteners 40). Individual fibers, tows, and/or ribbons may then be passed through adjacent channels 46 and through the outlet of nozzle assembly 18. Thereafter, cover 30 may be reconnected to base 29 (e.g., by insertion of fasteners 40). In some embodiments, the reinforcements may also need to be connected to a pulling machine (not shown) and/or to a mounting fixture (e.g., to an anchor point). Installation of the matrix material may include filling head 16 (e.g., reservoir 22 and/or channels 46 and/or coupling of an extruder (not shown) to head 16.

The component information may then be used to control operation of system 10. For example, the reinforcements may be pulled and/or pushed along with the matrix material from head 16. Support 14 may also selectively move head 16 and/or the anchor point in a desired manner, such that an axis of the resulting structure 12 follows a desired three-dimensional trajectory. Once structure 12 has grown to a desired length, structure 12 may be severed from system 10.

It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed system and head. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed system and head. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents. 

What is claimed is:
 1. A nozzle assembly for an additive manufacturing print head, comprising: a nozzle base having an opening configured to receive a plurality of continuous reinforcements; a cover configured to engage the nozzle base and close off a side of the opening; and a guide removably receivable within at least one of the nozzle base and the cover, the guide having at least one divider configured to axially divide the opening into a plurality of adjacent channels that each receive at least one of the plurality of continuous reinforcements.
 2. The nozzle assembly of claim 1, wherein: the guide is a first guide; and the nozzle assembly further includes a second guide that is swappable with the first guide, the second guide having at least one divider configured to axially divide the opening into a plurality of adjacent channels.
 3. The nozzle assembly of claim 2, wherein the plurality of adjacent channels of the second guide are different from the plurality of adjacent channels of the first guide.
 4. The nozzle assembly of claim 3, wherein the plurality of adjacent channels of the second guide are different in at least one of a number, a cross-sectional shape, a width dimension, a depth dimension, and a taper.
 5. The nozzle assembly of claim 1, wherein at least one of the plurality of adjacent channels tapers in at least one of a width direction and a depth direction.
 6. The nozzle assembly of claim 5, wherein the at least one of the plurality of adjacent channels tapers in both the width direction and the depth direction.
 7. The nozzle assembly of claim 1, wherein the plurality of adjacent channels each have one of a square cross-sectional shape and a rectangular cross-sectional shape.
 8. The nozzle assembly of claim 1, wherein the cover includes an inner surface coated with a low-friction material.
 9. The nozzle assembly of claim 8, wherein the guide is fabricated from the low-friction material.
 10. The nozzle assembly of claim 1, wherein the cover is L-shaped.
 11. The nozzle assembly of claim 1, wherein an edge of the guide at an outlet over which the plurality of continuous reinforcements pass is rounded.
 12. The nozzle assembly of claim 1, wherein a cross-sectional area at an outlet of each of the plurality of adjacent channels is smaller than a cross-sectional area at an inlet of each of the plurality of adjacent channels.
 13. The nozzle assembly of claim 1, wherein a depth and a width of each of the plurality of adjacent channels at an outlet is about 0.01 inch to about 0.10 in.
 14. The nozzle assembly of claim 1, wherein the nozzle base includes a recess configured to receive the guide.
 15. The nozzle assembly of claim 1, wherein the guide is configured to cause the plurality of continuous reinforcements to converge into a ribbon.
 16. A print head for an additive manufacturing system, comprising: a matrix reservoir; a nozzle base disposed downstream of the matrix reservoir and having an opening configured to receive a plurality of continuous reinforcements coated in a liquid matrix; a cover configured to engage the nozzle base and close off a side of the opening; a guide removably receivable within at least one of the nozzle base and the cover, the guide having at least one divider configured to axially divide the opening into a plurality of adjacent channels that each receive at least one of the plurality of continuous reinforcements; and a cure enhancer mounted at a trailing side of the nozzle base opposite the cover and configured to expose the matrix coating the plurality of continuous reinforcements to a cure energy.
 17. The print head of claim 16, wherein: the guide is a first guide; the print head further includes a second guide that is swappable with the first guide, the second guide having at least one divider configured to axially divide the opening into a plurality of adjacent channels; and the plurality of adjacent channels of the second guide are different from the plurality of adjacent channels of the first guide in at least one of a number, a cross-sectional shape, a width dimension, a depth dimension, and a taper.
 18. The print head of claim 16, wherein at least one of the plurality of adjacent channels tapers in at least one of a width direction and a depth direction.
 19. The print head of claim 16, wherein: the cover includes an inner surface coated with a low-friction material; and the guide is fabricated from the low-friction material.
 20. The print head of claim 16, wherein: the nozzle base includes a recess configured to receive the guide; and the guide is configured to cause the plurality of continuous reinforcements to converge into a ribbon. 